I. Field of the Invention
The invention relates to a counterbalance device and in particular to a counterbalance device for an articulated cover of a mail processing system.
II. Discussion of the Related Art
Mail processing systems for moving and printing postage on various pieces of mail are commonly known and often include a feeder module which feeds mailpieces to a mailing machine module. The mailing machine module includes either a mechanical or electronic postage meter which prints postage indicia and/or slogans on the mailpiece passing therethrough. The postage meter is usually mounted within a base portion of the maining machine module, as for example, is set forth in U.S. Pat. No. 4,876,956, issued to Riley, et al., which is hereby incorporated by reference. A lid or cover is articulately connected to the base portion of the mailing machine module and covers and protects the postage meter when in a closed position. The cover may also include function keys and displays through which information is communicated to and from the postage meter.
It is often the case however, that the cover is quite large and of significant weight. As the cover is moved through its full range of motion from a closed position to a fully opened position, the effective weight of the cover changes due to the angle it makes with respect to the base. Thus, the largest amount of force required to move the cover toward the fully opened position typically occurs when the cover is in the closed horizontal position. On the other hand, when the cover is substantially vertical to the base, a minimal amount of force is required to move it toward either the closed or opened positions. Beyond the vertical position, the effective weight of the cover once again continues to increase as the cover is moved toward the fully opened position. Due to the effective weight of the cover, there is a tendency for the cover to slam open with considerable force. The slamming open of the cover can ultimately cause damage to the cover, the base, and/or the articulating connection between the cover and the base. Consequently, counterbalance devices have been employed which are effective to minimize the differences in apparent weight of the cover as it moves from one operative position to another. Generally, these devices are effective to exert a force on the cover at any given intermediate position which is substantially equal and opposite to the effective weight of the cover so that when the cover is released in an intermediate position, the cover tends to stay in that intermediate position.
Known physical counterbalancing devices include an added, appropriately located weight on the opposite side of the cover pivotal axis. However, this type of counterbalance device adds a significant amount of weight and space requirements and increases the cost of the system. Other counterbalance devices utilize hydraulic or automatic cylinders. However, these counterbalance devices are costly, complex and subject to significant-maintenance problems. In addition, while the use of hydraulic shock absorbers or gas springs have been proposed, they are very expensive, present substantial space problems, and typically obstruct side access when the cover is lifted.
U.S. Pat. No. 4,571,775, issued to Leonard, discloses a counterbalance device which includes a complicated torsion member formed by a plurality of rods that are surrounded by a sleeve. The torsion member interacts with a cam via a follower arm and a follower roller in order to counterbalance the cover. The apparatus described in U.S. Pat. No. 4,571,775 is a complicated structure which is costly to produce and occupies a great deal of space. When the torsion member counterbalance device of U.S. Pat. No. 4,571,775 is incorporated within the base of a mailing module, a significant amount of space is utilized which cannot, for example, be used to incorporate additional stiffeners in the base. Thus, the base would have to be made out of stronger materials or enlarged and stiffened in a different manner.
Additionally, the torsion member apparatus of U.S. Pat. No. 4,571,775 focuses on providing neutral counterbalancing of the cover. By neutral counterbalancing, it is meant that the forces acting on the cover are in equilibrium at any point over the full range of movement of the cover such that the cover would remain in any position in which it was released. However, such a neutral force profile is not always desirable and a counterbalance device which is capable of easily varying the force profile exerted on the cover is needed to, for example, provide a force acting to keep the cover shut in the closed position while also providing a force acting to move the cover toward the closed position when it is in the fully opened position, thereby preventing the cover from slamming open under its own weight.